1. Field of the Invention
The invention concerns an angiographic process.
2. Description of the Prior Art
This process is customary in angiographic practice and affords the advantage that the vascular structures made recognizable in the viewing picture by the contrast medium are in sharp relief. In theory, the entire residual picture content could vanish; in practice, however, weak relief-like indications of other organ structures or bones persist on account of unavoidable differences in the conditions of photography, especially on account of the inevitable movements of the living vascular region. This facilitates orientation in studying the picture.
After instilling the contrast medium, a whole series of pictures is mostly taken at given time intervals, for example every 0.5 seconds, which are all processed into viewing pictures by photographic subtraction of a blank photograph or reference radiograph, so that the propagation of the contrast medium and possible obstructions in the vascular system may be recognized therein. Since this involves taking at least two, but usually many more pictures, there is considerable radiation exposure of the organism to be examined. This is particularly so when overexposure is practiced, as is often the case, to ensure obtaining usable photographs. Yet, details of diagnostic interest are often difficult to recognize, if at all, in the viewing picture, because of inadequate density differentials (differences of blackening) that are depicted.